Todd Lambert wrote in post #8997476
Hmm, not sure, but object distance shouldn't matter. It either front focuses or it back focuses which you can correct with MA. If it's doing something other than those, then yes, probably need to send it in.
No .. from my observation and testing of my 70-200 F4 and Tamron 60mm F2 macro. The distance to object (focus distance) do matters in some of the lens. For example, it is well know that the 70-200 image is soft (or actually cannot focus) at the minimum focus distance (MFD) of 1.2m at focal length of 200mm.
When I test the Tamron 60mm F2 macro, it is even worse. It focus ok at macro distance (0.3m-1m), then it becomes front focus as I step back (~1.5m), then it becomes back focus if I am very far away (>4m) from the object.
Now, I can understand why prime is preferred by some people. I think it is just technically a lot easier to make a prime that will focus properly, there is one less variable to play with. There are now 3 variables in zoom lens that can impact the image - the aperture, the focus distance, and the focal length.